Radios that can transmit and receive signals (that is, radio waves) are referred to as “two-way radios” or “transceivers.” Two-way radios that are handheld devices are usually called “walkie-talkies.” Other two-way radios include larger “mobile” devices—which are typically used in vehicles such as fire engines, ambulances, and police cars—and very large “base” or “base station” devices, which are usually used in fixed locations such as fire houses, ambulance-dispatch centers, and police stations. Various two-way radios are typically used together in “land mobile radio systems.” These LMR systems are commonly used by federal, state, and local first responders and emergency services; by public-works companies and other businesses; and by the military.
LMRs such as walkie-talkies usually cannot both transmit signals and receive them at the same time, and so they typically use “press to transmit” or “push to talk” (PTT) technology: when a button on the walkie-talkie is depressed, the device can transmit radio signals; when the button is released, the device can receive radio signals.
LMR or PTT communications using radio waves contrast with, for example, land-line telephone communications, which traditionally took place over telephone lines (such as wires and fiber-optic cables). But just as telephone communications can now take place over the Internet with networked phones using Voice over Internet Protocol (VoIP) technology, PTT communications can now take place over the Internet with networked radios using Radio over Internet Protocol (RoIP) technology.
Networked radios offer significant advantages over LMRs, but LMRs remain widely used by the military, first responders, and other groups. Some advantages of networked radios can be provided to systems using LMRs by using LMR-to-networked-radio conversion devices. For example, a Vocality V25 bridge/router can serve as an LMR-to-networked-radio conversion box. Such known conversion devices provide rudimentary functionality that permits two different LMR systems to communicate, which generally cannot be done unless the two systems are using the same frequency.
But communication problems can arise in both LMR-only systems and systems that mix LMRs with networked radios. Consider the example of an LMR-only radio system used by members of a fire department responding to a widespread forest fire. A fire-department captain may use a single walkie-talkie type LMR to communicate with several firefighters in the field who each have their own walkie-talkies. If the fire captain is a significant distance away from one or more of the firefighters, a fixed “repeater” or retransmission device located between the captain and the firefighters, such as a radio tower that already happens to stand in the affected area of the forest, can retransmit radio signals between them. But if a retransmission device is unavailable, the useful range of the LMR system is relatively limited.
It would be advantageous to provide RoIP devices (such as networked portable radios) and methods that permit such devices to operate more effectively with LMR devices (such as walkie-talkies). Specifically, it would be advantageous to provide devices and methods for a communications system in which a source device transmits a voice communication to one or more destination devices by: (1) permitting communications among users with RoIP devices or LMR devices or both; (2) using one of the devices in the communications system as a retransmission device; (3) actively managing information about the number and type of LMRs in the system; (4) avoiding limitations on the number and type of LMRs in the system; and (5) when there is more than one LMR present that can act as a retransmission device, having the system make the best choice possible so that as many LMR-only users as possible hear the transmitted voice communication.